1. Field of the Invention
The present invention relates to a high frequency semiconductor integrated circuit realizing a good high frequency characteristic by changing a combination of plural circuits according to performance or application.
2. Description of the Background Art
Referring to FIG. 22, a prior art high frequency semiconductor integrated circuit 600 includes a main circuit 610 and a circuit block 620.
Main circuit 610 includes an input terminal 6101, a transistor 6102, transmission lines 6103 and 6104, and an output terminal 6105. Transistor 6102 is connected to input terminal 6101 at its gate terminal, to a ground node 7 at its source terminal, and to transmission line 6103 at its drain terminal. Transistor 6102 is, to be specific, a field effect transistor such as a MOS FET, or a MES FET (Metal Semiconductor Field Effect Transistor), HEMT (High Electron Mobility Transistor) or HET (Heterojunction Bipolar Transistor) made from GaAs.
Transmission lines 6103 and 6104 are connected in series between the drain terminal of transistor 6102 and output terminal 6105. Transmission lines 6103 and 6104 are each an interconnect having a predetermined length and a predetermined width and formed by patterning in fabrication of high frequency semiconductor integrated circuit 600.
Circuit block 620 includes passive circuits 6201 and 6202 and a capacitor 6203. Passive circuits 6201 and 6202 and capacitor 6203 are connected in series between a node 6106 of main circuit 610 and ground node 7. Passive circuits 6201 and 6202, for example, are each configured such that a resistor, a coil and a capacitor, which are passive elements, are connected in series with or in parallel to each other. That is, passive circuits 6201 and 6202, used together with capacitor 6203, each include a circuit of a configuration in which a resistor, a coil and a capacitor are combined in a proper manner such that when an input signal inputted to input terminal 6101 is outputted from output terminal 6105 in main circuit 610, output matching, efficiency matching, gain matching and distortion matching can be achieved.
Main circuit 610 receives an input signal having a frequency in the range of microwaves or milliwaves at input terminal 6101 and outputs the received input signal from output terminal 6105 through transistor 6102 and transmission lines 6103 and 6104.
In a case where passive circuits 6201 and 6202 of circuit block 620 are each constituted of a passive element optimized for output matching, main circuit 610 performs output matching and outputs an input signal inputted at input terminal 6101 from output terminal 6105. Furthermore, in a case where passive circuits 6201 and 6202 are each constituted of a passive element optimized for efficiency matching, main circuit 610 performs efficiency matching and outputs an input signal inputted at input terminal 6101 from output terminal 6105.
In prior art high frequency semiconductor integrated circuit 600, however, circuit block 620 is connected to node 6106 of main circuit 610; therefore, when only main circuit 610 is desired to be used, or when a high frequency semiconductor integrated circuit having a different performance is requested, a problem arises since separate circuit patterns are required. That is, when passive circuits 6201 and 6202, each constituted of a passive element optimized for output matching, are incorporated into circuit block 620, only main circuit 610 cannot be used and further, high frequency semiconductor integrated circuit 600 cannot be differently used as a high frequency semiconductor integrated circuit for achieving efficiency matching.
Furthermore, once a circuit pattern is formed on a semiconductor substrate, a circuit block cannot be adjusted if variations occur in performance of an active element, leading to another problem of decrease in product yield of a high frequency semiconductor integrated circuit.